Grinding device



H. R1 BILLETER GRINDING DEVICE Sept. 1, 1959 Filed Aug. 30'I 1956 F j l 1639 36 2 Sheets-Sheet 1 5,9 Guam/L,

Unit States 2,901,869 Patented Sept. 1, 1959 GRINDING DEVICE Henry Robert Billeter, Deerfield, lll., assignor to Amm'co Tools, Inc., North Chicago, Ill., a corporation 'of Illinois Application August '30, 1956, Serial No. 607,079

7 Claims. (Cl. S1-96) This invention relates to a grinding device, and more particularly to a device for forming an arcuate contour by a grinding operation and having means for correctly positioning a brake shoe therein. One important application of such a device is the dressing down of automotive brake shoe linings. Accordingly, the present invention is disclosed in connection with an automotive brake shoe lining grinder.

Devices for grinding the linings of automotive brake shoes to a predetermined arcuate contour currently include a rotating grinding element and a workpiece holder adapted to pivot the workpiece in an arc of contact with the grinding element about a pivot which is adjustable toward and away from the grinding element. Accessory to or integral with such a grinding device is an arm having an adjustable abutment for the anchor recess or eye of a brake shoe for positioning the shoe in the device. The shoe positioning arm with its adjustable abutment permits all the brake shoes of a set to be positioned in the workpiece holder of the grinding device in like manner, enabling them to be ground so as to match or be similar, either using a first one of the shoes as the model for setting the arm abutment, or setting the abutment by visual inspection. Of course, if the grinding device is badly set up to grind the initial shoe, as by means of an improper initial setting of the abutment, then all the shoes will be incorrectly ground. When the shoe is that of an adjustable anchor brake assembly, such a grinding error does not always require that the lining be scrapped, for the position of the anchor in the assembly can be adjusted to counterbalance the grinding error so that the processed shoe will properly engage its brake drum. Obviously, however, a grinding error is undesirable in that the resultant lining thickness is not uniform throughout the shoe length and will wear out sooner at the thin end.

On the other hand, minor grinding errors on a brake shoe of a brake assembly of the iiXed anchor type are completely undesirable not only with respect to the life of the lining, but to the proper functioning of the brake assembly as well. Since the anchor of this type assembly is non-adjustable, there is no way to adjust out any grinding error, and an improperly ground lining will e11- gage the drum improperly.

The operation of the grinding devices hereinabove discussed includes an initial adjustment of the pivot toward or away from the grinding element so that the distance between the pivot axis and the closest point of the grinding element will be equal to the radius of the brake drum for the shoe to be processed. Next, the anchor eye abutment is adjusted by visual inspection so that the brake lining will be generally centered relative to the grinding element, and the brake shoe is clamped in the workpiece holder in such mannerithat the generating center of the shoe arc coincides with the pivot axis. Finally, and without disturbing the pivot location, the workpiece holder, together with the supported shoe, is advanced radially of the pivot and toward the grinding element suiiciently to dress down the entire arcuate length of the lining upon a pivoting of the workpiece holder.

It will be seen that since the pivot remains undisturbed while the center of radius of the shoe arc is advanced upon an advance of the shoe, the centers of radii of the arcuate shoe contour and of the contour formed on the lining will be displaced from each other. If this displacement does not lie on a line perpendicular to a shoe radius through the anchor eye about which the shoe pivots, which line also generally represents the radial bisector of the-arcuate contours, one end of the lining will contact its-brake drum, on brake actuation, prior to the other lining portions unless the shoe position in the brake assembly can be adjusted, as by means of an adjustment of the anchor of the assembly, to compensate for the displacement of the lining center.

An object of the present invention is to provide a device for so grinding an automotive brake shoe lining that neither end of the processed lining will contact a brake drum corresponding thereto before another portion of the lining when the shoe is actuated pivotally about the brake assembly anchor.

Another object is to provide an automotive brake shoe lining grinding device having a pivoted workpiece holder, an anchor eye positioning abutment, and means for setting the latter to a position relative to the workpiece holder pivot corresponding to the position of the anchor in the brake assembly of a shoe to be ground.

Yet another object is to provide a pivotally fed grinding device having an anchor eye positioning abutment and a gauge for setting the latter to enable the grinding of automotive brake shoe linings with a minimum amount of error.

A further object is to provide a gauge for setting the anchor eye positioning abutment of a pivotally fed automotive brake shoe lining grinding device in lateral alignment with a predetermined distance from the pivot.

Other objects and advantages of the present invention will appear from the detailed description thereof hereinbelow set forth, taken in connection with the appended drawings, in which:

Fig. l is a side elevational view of a grinding device constructed in accordance with the principles of the present invention;

Fig. 2 is a fragmentarytop plan view of the grinding device of Fig. l;

Fig.- 3 is an enlarged perspective view of the gauge element of the present invention;

Fig. 4 is an enlarged fragmentary plan view of the grinding device of Fig. 2;

Fig. 5 is an enlarged fragmentary side elevational view of the grinding device of Fig. 1;

Fig. 6 is a fragmentary sectional view taken substantially on line 6-6 of Fig. 4;

Fig. 7 is a fragmentary sectional view taken substantially on line 7-7 of Fig. 4; and

Fig. 8 is a perspective view of a modified form of gauge element.

The grinding device herein described and claimed is similar to, and an improvement of the device disclosed and claimed in my Patent No. 2,734,319, dated February 14, 1956, to which reference may be had for a detailed disclosure of the construction, operation, and inventive concept underlying elements common to both that device and the present invention.

4 Referring now to the drawings, and in particular to Figs. 1 and 2 thereof, a grinding device is shown for processing the linings of automotive brake shoes, and incorporating the inventive principles disclosed and claimed herein. The device includes a base 10 in the form of an elongate rectangular casing-like member having a top wall which constitutes a bed plate 12 upon which are mounted the principal operating elements of the device. An electric motor 14 is supported within an opening in the top wall of the base and is drivingly connected to a cylindrical grinding yelement 16 mounted on the base and adapted toy dress down the surface of a brake shoe lining. A carriage 18 is slidably supported on the bed plate 12- for adjustable movement toward and away from the grinding element 16, and carries a turntable 20 mounted thereon as to -be pivotable about a pivot pin 22 upstanding from the carriage. The turntable includes an upstanding body portion 24 having a pair oftransversely spaced bearings 25 formed therein.

A workpiece holder 26 is removably mounted on the turntable 24 and includes a holder base 28 from which a pair of elongate guide rods 30 and 31 fixedly project. The guide rods 30 and 31 are transversely spaced complementally to the turntable bearings 25 and are adapted to be received Within the spaced bearings 25 to support the workpiece holder 26 on the turntable. The workpiece holder further includes a clamping jaw 32 pivotally mounted on the holder base 28 and adapted to be manually clamped thereagainst by means of a manipulating knob 36. v

- The workpiece holder 26 is adapted to clamp to flange F of an automotive brake shoe BS to support the latter for processing engagement of the lining L with the grinding element 16.- A pair of shoe locating studs 38 project rearwardly from the holder base 28 to provide a two-point means of positioning an arcuate brake shoe in a workpiece holder so that the center of radius of arcuate shoe contour coincides with the axis of the pivot pin 22.

Means are provided for adjusting the position of the workpiece holder 26 on the turntable body 24 and include an elongate feed screw 40 pivotally and rotatably connected to the holder base and projecting forwardly therefrom. The feed screw 40 includes a threaded portion 42 adapted to be removably engaged with the threads of a half nut 44 fixed to the top surface of the turntable body, and further includes a manipulating handle 41 to facilitate operation thereof. The feed screw 40 provides an accurate means of .moving the workpiece holder 26 rearwardly from the turntable by means of rotation of the feed screw when the threaded portion thereof is in engagement with the half nut 44, as well as a convenient means of pivoting the turntable and workpiece holder as a unit about the pivot pin 22.

Abutment means are provided to cooperate with the shoe locating studs 38 for properly positioning a brake shoe BS in the 'workpiece' holder and include an arm 52 mounted on the spaced guide rods 30 and 31 by suitable means. Preferably, the arrn 52 is removably mounted on the support rods as by clamping means including a strap 54 adapted to be tightened down on the arm 52 sandwiching the guide rods therebetween. To this end a screw member 56 is rotatably carried through the strap 54 and in threaded engagement with the arm 52. A manipulating pin 58 is mounted transversely in the head of the screw member 56 to facilitate the tightening down of the strap 54 against the guide rods 30 and 31.

The arm 52 has a first portion 60 projecting generally parallel to the :guide rods and carrying an upstanding boss 62 on the tip thereof. An elongate strap 64 having a longitudinal slot 66 intermedate its width is mounted horizontally on the top surface of the boss 62 and is retained thereon by 'a screw 68 having an enlarged head 70` for angular and sliding adjustment thereon. The

shank of the screw 68 is loosely carried in the slot 66 engage the anchor eyes of the majority of the automotive brake shoes currently in use. Preferably the pin 78 has a radius of .405 inch, a radius common for the anchor eyes of the majority of makes of brake assemblies. The pins 79 and 80 are of larger diameters respectively and provide means of matching the anchor eyes of other brake shoes. It can be seen that the strap 64 provides a means by which an anchor eye abutment or pin of the correct diameter may be adjustably positioned to provide an abutment for the anchor eye of a brake shoe to be processed. As hereinabove described, the projecting studs 38 furnish a means of properly locating the center of radius of the arcuate contour of the brake shoe, while the pin 78 or its complemental members 79 and 80 cooperate with the studs to provide a means for positioning the brake shoe in proper angular relation with the direction of movement of the workpiece relative to theturntable and along the guide rods 30 and 31.

A gauge 90 provides a means by which a preselected anchor eye engaging pin may be accurately and correctly positioned for a particular shoe to be processed. The gauge for each particular size and make of brake shoe to be processed is suitably Iformed as a generally T-shaped one-piece member. The gauge includes an elongate pin-positioning arm 92 provided at one end with an arcuate recess 93 adapted to snugly accommodate the pin 78 complemental thereto and complemental to the brake shoe to be processed, the pin-positioning arm being further provided with a downwardly depending ange 94 for purposes hereinafter set forth. There is a variance in the anchor to brake center distances among different makes of brake assemblies, as well as a variance in the radii of the arcuate eyes of the shoes thereof, for

be adapted to accommodate and position one of these additional pins 79 or 80 a predetermined distance from the pivot for a particular make of brake assembly. A second or body arm 96 extends generally perpendicularly to the pin positioning axrn 92 and is of slightly greater length than the turntable body 24. A downwardly depending second ange 98 is provided at the forward end of the body ann 96, both of the lianges 94 and 98 having axially aligned arcuate recesses 97 and 99 re1- spectively adapted to firmly accommodate the guide rod 30 therein.

The gauge is adapted to be positioned on the workpiece holder in longitudinally straddling relation with the turntable body 24 and so as to support the pin positioning arm 92 in the desired elevational position relative to the positioning pin 78. Accordingly, the alnge 94 includes a bearing surface 100 adjacent the second end 102 of the pin positioning arm 92. This bearing surface 100 is in elevational alignment with the arcuate recess 97 in the liange 94 such that when the recess 97 is in accommodating engagement with the guide rod 30, the bearing surface 100 engages the second guide rod 31 to support the pi.n positioning arm 92 in a substantially horizontal position. Y

The flange 94 has an extension 108 which carries a lug projecting forwardly therefrom. The lug is adapted to abut the head of the pivot pin 22 of the turntable 20, and, accordingly, is positioned intermediate the points of association between the arcuate recess 97 and the bearing surface 100 with the guide rods 30 and 31 respectively. The lug 110 projects a predetermined distance from the ange extension 108 to position the gauger90 and particularly the pin positioning arm 92 thereof such that when the ange recesses 97 and 99 are accommodated on the guide rod 30, the pin engaging recessl 93 in one end of the pin positioning arm Wil-l be centered on a line perpendicular to the guide rods 30 and 31 and passing through the axis of the pivot pin 22.

The recesses 97 and 99, as well as the lug 118, are so positioned relative to the pin engaging recess 93 that when the former are in engagement with the guide rod 30 and the lug abuts the head of the pivot pin 22, the distance between the axes of the pivot pin and of the positioning pin 78 when the latter is accommodated within the recess 93 is equal to the distance between the brake drum axis and the axis of the anchor of the brake assembly to which the brake shoe to be processed corresponds.

By Way of dimensional example of a grinding device constructed in accordance with the principles of the present invention and including a gauge adapted to process the brake shoes of a 1955 Nash Statesman automobile, or a 1955 Hudson Wasp automobile, the brake shoes of both of which automobiles have a length of 4.187 inches between the centers of the shoe and of the anchor eye thereof, the guide rods Sil and 31 are so spaced and centered relative to the pivot pin 22 that the distance perpendicularly from the axis of the pivot pin to the axis of the guide rod 30 is 1.250 inches. The arcuate recesses 97, 99 and 93 of the gauge are so positioned that when the recesses 97 and 99 are accommodated on the guide rod 30 and the positioning pin 78 is accommodated in the recess 93, the perpendicular distance between the positioning pin axis and the guide rod axis is 2.937 inches. Therefore it can be seen that when the gauge 90 corresponding to the brake shoes of the makes herein described by way of example is properly positioned on the workpiece holder, and the anchor eye positioning pin 78 is adjusted so as to be rigidly accommodated within the recess 93, the distance between the axis of the pivot pin 22 and the axis of the positioning pin 78 will be 4.187 inches, and equal to the corresponding :distance in the complemental brake assembly.

When a brake shoe is mounted in the workpiece holder with the anchor eye thereof in engagement with the positioning pin 7 8, and with the lining L of the brake shoe in contact with the grinding element, the arcuate center of the lining will coincide with the axis of the pivot pin 22, and a line through the pivot pin axis and parallel to the direction of movement of the workpiece hold'er relative to the turntable will bisect the lining. When so positioned, the lining L will be fed toward the grinding element along the bisecting line, and will maintain the desired positional relationship between the arcuate contour formed on the lining and the axis of the anchor in the brake assembly about which the shoe pivots when actuated.

A brake shoe lining so processed and originally positioned with the center of the arcuate anchor eye positioned on a line perpendicular to the direction of movement of the workpiece holder relative to the turntable and passing through the axis of the pivot pin 22 will be processed with only a minute error therein proportional tothe increase in length of the distance between the axis of the pivot pin 22 and the axis of the positioning pin 78 as the workpiece holder and the pin 'i8 are moved relative to the pivot pin. lt will be recalled that the movement of the workpiece holder is such as to advance the lining L into contact with the grinding element so that upon a pivotal feeding of the lining about the pivot pin 22 a dressing down of the complete arcuate extent of the lining will result. Since the advancing feed of the shoe is very slight, the increase in distance between the axis of the positioning pin 7S and the axis of the pivot pin 22 will also be correspondingly negligible. However, provision may be made to compensate for this slight error by locating the recess 93 for the positioning pin a predetermined distance forwardly of a line which is perpendicular to the direction of advancing movement of the workpiece holder and which passes through the axis of the pivot pin 22, so that the estimated distance through which the workpiece holder will be advanced will be bisectedby that perpendicular line, whereupon the distances between the axes of the positioning pin 78 and pivot pin 22 before and after movement of the workpiece holder will be equal, and the lining L will be processed to have an arcuate contour formed thereon in desired position relative to the anchor of the brake assembly.

yIt can be seen that the gauge is adapted to combine with the other elements of the grinding device to easily and accurately indicate the proper position for an anchor eye engaging pin. The grinding device is set up for the processing of a brake shoe lining by initially adjusting the position of the carriage 18 on the base 10 to establish a distance between the axis of the pivot pin 22 and the closest point thereto on the grinding element 16 corresponding to the internal radius of the brake drum to which the shoe to be processed corresponds. Once the proper location of the pivot pin has been established, the brake shoe to be processed is clamped in the workpiece holder 26 either in reversed position, or with the anchor eye thereof otherwise angularly removed from the general area where it should be located to properly position the brake shoe in the workpiece holder. This aiords an open space within which the anchor eye positioning pin may be adjusted. The workpiece holder is then advanced or retracted radially from the pivot pin 22 by rotation of the feed screw 40 in engagement with the half nut 44 until the surface of the lining establishes proper grinding contact with the grinding element.

Upon the proper positioning of the pivot pin 22 and of the brake shoe lining relative to the grinding element 16, the proper location of the anchor eye positioning pin 78 is determined by use of the gauge 90. The gauge is positioned on the workpiece holder in overlying, straddling relationship longitudinally of the turntable body, and with the recesses 97 and 99 accommodated on the guide rod 30. The gauge is further positioned relative to the workpiece holder to rest the bearing surface 100 on the second guide rod 31, whereupon the gauge is moved forwardly until the lug abuts the head of the pivot pin 22. When the recesses 97 and 99, the bearing surface 100, and the lug 110 are thus positioned on the iirst guide rod 30, the second guide rod 31, and relative to the pivot pin 22, the pin positioning arm 92 will extend horizontally and transversely of the workpiece holder and in register with the pivot pin. The correct position for the pin 78 is indicated by the recess 93 in the end of the pin positioning arm 92. The pin 78 is adjusted to engage the recess 93 by loosening the screw 68 to loosen the strap 64, whereupon the strap can be adjusted on the boss 62 along the extent of the slot 66, as well as pivoted relative to the screw 68. When the pin 78 is iirrnly positioned, as by means of a tightening down of the screw 68, the brake shoe is released from its initial, temporary position in the workpiece holder and repositioned such that the brake shoe rim R engages the studs 38 and the anchor eye engages the pin 78.

By way of modiiication of the present invention, the grinding device may include means for mounting the workpiece holder on the turntable body other than the transversely spaced guide rods hereinabove disclosed. As for example, the mounting of the workpiece holder may include a single elongate guide rod (not shown) having a diamond shaped or other polygonal cross-section and slidably carried by the turntable body, such as shown in my Patent No. 2,715,799, granted August 23, 1955. The guide rod of polygonal cross-section serves to support the workpiece holder rigidly on the turntable body against all relative movement except a sliding adjustment along the elongate extent of lthe rod. The gauge for a grinding device having such mounting means for the workpiece holder has the general form hereinabove disclosed, but is modified in obvious manner to provide recesses adapted to accommodate the polygonal cross-section of the guide rod to provide not only a locating means transversely of the guide rod but also a means of connecting the gauge to the guide rod so as to support the pin positioning arm thereof horizontally.

7 Y Further modiication may be made by way of change of form of the pin about which the turntable and the supported workpiece holder pivot. For example, the pin may have a substantially elongate form and project vertically up from the turntable. In this event the gauge is complementally modiiied in obvious manner to provide a recess or other means for engaging the pivot pin so as to locate the pin positioning recess of the gauge a predetermined distance from the turntable pivot pin and in lateral alignment therewith.

A gauge 190 embodying the modifications abovedescribed is shown in Fig. 8, which gauge is similar in all respects to the gauge 90, except that the aligned recesses 197 and 199 are right-angled in form instead of arcuate, in order to receive a guide rod of square cross section and the pin-positioning arm 102 is provided with an arcuate recess 211 to receive an extended type pivot pin (not shown).

Even further, it will be apparent that a grinding device may be provided with a series of gauges of differing shapes and sizes in order to adapt the device to receive brake shoes of the wide variety of sizes and makes currently in use.

The grinding device hereinabove disclosed provides an inexpensive and compact apparatus for processing brake shoe linings so as to impart thereto true arcuate contours correctly positioned relative to the anchor eyes thereof. A brake shoe so processed will engage its brake drum correctly upon being actuated pivotally about the anchor when repositioned in the brake assembly with the anchor eye thereof in pivoting engagement with the anchor in the brake assembly. That is to say `that neither end of the arcuate extent of the lining will contact the brake drum prior t-o any other portion of the lining.

The grinding device is adapted to process a complete set of brake shoes with but a single, easily effected set-up of the device, thus enabling a complete processing operation for all the shoes of a vehicle to be quickly and conveniently accomplished. The gauge provides a simple yet novel means by which the anchor eye positioning abutment of the basic grinding device is quickly and easily positioned in lateral alignment with and a predetermined distance from the pivot pin of the turntable, while a correctly-positioned anchor eye abutment enables a brake shoe to be properly mounted in the device for accurate feeding into a grinding element,

I claim:

l. In combination, a grinding device comprising a base, a grinding element mounted on said base, a carriage mounted on said base for adjustable movement toward and away from said grinding element, a turntable mounted on said carriage and rotatable thereon about a pivot, a workpiece holder mounted on said turntable for adjustable movement thereon in a direction radially of said pivot, and a workpiece positioning abutment adjustably connected to said workpiece holder adapted to engage the anchor eye of an automotive brake shoe, and a gauge for setting the workpiece positioning abutment, said gauge comprising a body member including a first portion having a pair of spaced edges each engaging said workpiece holder a predetermined distance from said pivot, a second portion spaced from said iirst portion and having an edge engaging a portion of the workpiece holder, a third portion having locating means engaging the workpiece positioning abutment and spaced a predetermined distance from the edges of said iirst portion and in lateral alignment with said pivot relative to the direction of movement of the workpiece holder radially of the pivot, and a fourth portion engaging said pivot to position said gauge longitudinally of the direction of movement of the workpiece holder.

2. A gauge for use with a brake shoe grinder of the type having a grinding element, a pivot adjustable toward and away from `the grinding element, a turntable pivotally supported for swinging movement about the pivot, a workpiece holder slidably mounted on the turntable for feed movement in a direction diametrically thereof and a workpiece positioning abutment provided with an anchor-eye positioning abutment and carried on the workpiece holder for movement therewith and for adjustment thereon in both a direction parallel to and laterally of the direction of feed movement, said gauge comprising a rigid member having mutually spaced rst and second supporting surfaces adapted to engage the workpiece holder and support the gauge thereon, a gauging surface displaced laterally from a line through said first and second supporting surfaces and adapted to engage and locate the anchor-eye positioning abutment of the grinder, a third supporting surface spaced laterally from the line through said first and second supporting surfaces and adapted to engage the workpiece holder and maintain the gauge against tilting thereon, and a gauge positioning surface spaced from said other surfaces adapted to engage the pivot of the grinder and position the gauge on the workpiece holder in the direction of feed.

3. A gauge for use with a brake shoe grinder of the type having a grinding element, a pivot adjustable toward and away from the grinding element, a turntable pivotally supported for swinging movement about the pivot, a workpiece holder slidably mounted on the turntable for feed movement in a direction diametrically thereof and a workpiece positioning abutment provided with an anchor-eye positioning abutment and carried on the workpiece holder for movement therewith and for adjustment thereon in both a direction parallel to and laterally of the direction of feed movement, said gauge comprising a rigid member having mutually spaced iirst and second supporting surfaces having recesses therein respectively and adapted to engage the workpiece holder and support the gauge thereon, a gauging surface having a recess displaced laterally from a line through the recesses in said iirst and second surfaces and adapted to engage and locate the anchor-eye positioning abutment of the grinder, a third supporting surface spaced laterally from the line through the recesses in said iirst and second surface and adapted to engage the workpiece holder and maintain the gauge against tilting thereon, and a gauge positioning surface spaced from said other surfaces adapted to engage said workpiece holder and position said gauge thereon.

4. A gauge for setting an anchor-eye positioning abutment of a brake shoe grinder, said gauge comprising a rigid member having a pair of mutually displaced, aligned gauge-supporting and positioning recesses, a gauge supporting surface displaced laterally from a line through said gauge supporting and positioning recesses, a gauging recess displaced laterally from said line, and a gauge positioning surface displaced from said recesses and said surfaces.

5. A gauge for setting an anchor-eye positioning abutment of a brake shoe grinder, said gauge comprising a rigid member having an abutment-positioning arm with a recess at one end, a body arm extending generally perpendicular from said abutment-positioning ann and in the same plane, a iirst support extending from said positioning arm and generally perpendicular to said plane and having a recess in its outer portion and a supporting surface spaced from said recess and at the same distance from the plane of said body arm as the bottom of said recess, a lug projecting inwardly from said first support at a location intermediate said second recess and said supporting surface, and a second support extending from the end edge of said body arm remote from said abut ment-positioning arm, generally parallel to and in the same direction as said first support.

6. A gauge for setting an anchor-eye positioning abutment of a brake shoe grinder, said gauge comprising a rigid member having an abutment-positioning arm with an abutment-engaging surface at one end, a body arm extending generally perpendicular from said abutmentpositioning arm and in the same plane, a first supporting portion extending from said abutment-positioning arm and generally perpendicular to said plane and having spaced support-engaging surfaces at its outer portion at the same distances from the plane of said body arm, a lug projecting inwardly from said rst supporting portion at a location intermediate said support receiving surfaces and said engaging surface, and a second supporting portion extending from said body arm remote from said abutment-positioning arm generally parallel to and in the same direction as said rst supporting portion.

7. A gauge for setting an anchor-eye positioning abutment of a brake shoe grinder, said gauge comprising a single rigid member of sheet material having an abutment-positioning arm with a notch in one end edge5 a body arm extending generally perpendicular from a rst side edge of said abutment-positioning arm and in the same plane, a first flange extending from a second side edge of said abutment-positioning arm and generally perpendicular to said plane and having a notch in its free edge and a supporting edge portion spaced from said notch and at the same distance from the base of said flange as the bottom of said notch, a lug projecting inwardly from said first flange at a location intermediate said second notch and said supporting edge portion; and a second ange extending from the end edge of said body arm remote from said abutment-positioning arm, generally parallel to and in the same direction as said first flange.

References Cited in the file of this patent UNITED STATES PATENTS 602,778 Shimer Apr. 19, 1898 1,919,545 Fisher July 25, 1933 FOREIGN PATENTS 938,216 Germany Jan. 26, 1956 

